RISK ESTIMATES FOR DEVELOPING MOTOR-NEURON DISEASE IN FIRST-DEGREE RELATIVES

Patients with motor neurone disease resident in the three counties of South Glamorgan, Mid Glamorgan and Gwent (total population 1 394 400) from 1/11/91 to 31/12/92, were ascertained through general practitione rs and neurology department records: 62 out of 71 (51 male, 20 female) index cases ascertained agreed to be visited. These individuals were clinically reviewed, had a detailed family history taken and, after di scussion, had a blood sample taken for testing for the X-linked bulbos pinal muscular atrophy mutation. The period prevalence of motor neuron e disease was 5.02/100 000 with a mean age of onset of 59.4 (S.D. 12.9 ) years. One 66-year-old male was found to have the X-linked bulbospin al muscular atrophy mutation. A single, definite first-degree relative pair was identified, of whom only one was included in the data. The i ndex cases had a total of 131 offspring and 173 siblings. The risk est imates, by current age, for these first-degree relatives of patients w ith apparently sporadic motor neurone disease decreased from 1 in 85 a t age 20 years to I in 1683 at age 80 years. These estimates require c onfirmation in an independent sample, as they are based on a single '' event''.